I just get LaTeX source code from my friend for one of the lectures in Germany. Is there any easy way to translate the German document into English?I would like to give a example of what I am going to translate.

I hope the mathematical content is ok, because there are several mistakes in grammar in this short text, and "rehlifizierbar" doesn't exist.

For automated translation, one could process the HTML or PDF or TXT output (pdftotext) with a standard translator tool or with google translate. As Clemens, I think there's no way yet of translating directly within LaTeX markup.